Cement compositions and cementing operations



United States Patent ()fiFice 2,695,669 Patented Nov. 30, 1954 .ziasxaaCEMENT COMPOSITIONS AND CEMENTING PERA ON Carroll v. Sidwell, Tulsa,Okra;

Nb Drawing. Application June 16, 1953, .,,s 1. .3 z,15

2o ciaiiiis. ct 136 29 This is a continuation in part of my copendingapplication Serial No. 160,585,;filed May 6, 1950, and now abandoned. V

This invention relates to cement compositions and cementing operationsand more particularly to a readily pumpable cement composition andmethod of handling cement compositions which is especially useful incementing oil and gas wells or the like. In drilling oil and gas wellsit is frequently necessary to cement the well casing or in cases wherecirculationof the, drilling fluid has been lost and cannot be restoredto seal the openings through which the circulation is lost with a cementplug or block. It is desirable that .the weight of. the cement be keptat a minimum, limited however by the need for maintaining a certainamount of resistance to compression and the need for a very lowpermeability to fluids contained in the well hole after the cement isset. It is also necessary that the] cement be pumpable in order to beintroduced into the ,well hole. Present practice in cementing oil andgas wells-is to use a slurry of Portland cement, gypsum cement orotherquick-hardening cement in water either alone or admixed withcertain bulking agents such as cane-fibre, wood fibres, cellophane,cotton seed hulls, etc. Care must be taken however in making additionsof bulking agents to cements since their addition in most instancesincreases the viscosity markedly and in some types of bulking agents thetendency to bulkup? in the drill pipe is so great that the amount whichmay be added is very small. In the case of certain organic bulkingagents the products of reaction and decomposition attack thecementlcausing it to deteriorate after a relatively short period oftime. For example, sugar cane fibre may decompose producing productswhich will attack and cause the cement to deteriorate within a matter ofa few months.

The use of cement alone or in combination with many of theaforementioned bulking agents under high pressure frequently results inpremature dehydration of the cement and consequent loss of its mobility.This appears to be caused by separation and agglomeration of the cementparticles from the slurry by their own weight or by the water filteringaway from the cement particles into porous or. fractured zones. Cementwhich has been thus prematurely dehydrated cannot be moved into positionaround the well casing in casing cement jobs or into the zone of lostcirculationwhere the purpose of the cement is to prevent such losses.

In addition to the difficulties mentioned above, it has been found thatthe producing zones of certain oil fields are located below or betweencorrosive brine zones which attack and destroy the well casing, whichsame brines will attack ordinary oil well cements resulting in theirdestruction within a short period of time.

In placing ordinary oil Well cements it is the general practice toremove the excess wall cake formed by the drilling fluid in the wellhole by the use of mechanical scratching devices attached to the casing.This practice is necessary in order to increase the effectiveness of.the cement, to reduce channeling and contamination of the cement slurryandto get a satisfactory bond between the cement and the wall of the.well hole. The use of such scratchers, however, requiresthe raising,lowering and in some cases, the rotation of the casing. This practice ishazardous and undesirable since movement of the casing in this fashionfrequently results in failure and fracture of the casing, the reopeningof a previously sealed; porous formation and consequently lossofcirculation or causes a large amount of material to break away from the'wallo'f the well bore and choke the bore any of which might make itnecessary to abandon the entire operation.

I have found a material and a method for cementing oil and gas wells andthe like which have proven to be far superior to any presently knownmethod or material for cementing operations in oil and gas wells or thelike. Tests have shown that the cementing material of my invention mayhave a relatively light weight yet have suificiently high compressivestrength. The material of this invention has been found to resist thecorrosive influences of brines which destroy ordinary well cements andcasing and itself does not contain materials which will decomposethereby deleteriously affecting the life of the hardened aggregate. Thismaterial has been found to have a high insulating factor approachingthat of cork which is particularly important in wells that are subjectto great temperature change inside the casing due to the cooling effectof expanding gas. It has also been found that the cement of thisinvention will act as its own scouring agent to remove excess wall cakein the well and thus avoid the extra hazard of moving the well casingand the possibility of opening a porous formation with subsequent lossof circulation. Moreover, the cement composition of my invention resistspremature dehydration and loss of mobility.

I have discovered a cement composition for well drilling comprising ingeneral a mixture of cement and expanded volcanic rock, or cement,volcanic rock and bentonite in certain proportions which is relativelylight in weight, has sufficiently high compressive strength, will resistdeterioration in the well hole, and will give a better bond to the wallof the hole.

I have found, that when these materials are admixed in properproportions with water they will produce a slurry WhiCh'Wiii be light inweight and can be readily pumped into the well hole. A suitable mixturefor most well cementing purposes will have a compressive strength inexcess of 1,000 lbs. per square inch and is made up of cement, bentoniteand expanded volcanic rock in the broad proportions of between about onepart of cement to from about 0.1 to 8 parts of expanded volcanic rock byvolume to cement and 0. to 10% by weight of bentonite on the weight ofthe cement. A cement composition having narrower ranges of compressivestrength, mobilityand weight can be produced by'admixing cement andexpanded volcanic rock in the proportions -of about 110.5 to 1:2 byvolume of cement with from 0. to 10% by weight of bentonite on theweight of the cement.

In applications where the thixotropic properties of bentonite are notneeded or desired the bentonite may be omitted and the mixture of cementand expanded volcanic rock used alone.-

My preferred mixture however, for general use, comprises a mixture ofcement and expanded volcanic rock in a ratio of about 1:1 by volume withabout 5% by weight of bentonite on the weight of the cement.

In order to produce a slurry which may be pumped into the well hole theabove compositions are added to a sufficient amount of water to producea pumpable mixture. I have found that when any of the aforementionedcompositions are added to an amount of water equal to about 40% to byweight of the weight of the cement, a satisfactory and pumpable slurrywill be produced. Such a slurry should preferably have a viscosity notexceeding 40 poises, although under some conditions of well boresapparent higher viscosities may be desirable. V

The cement used in the practice of my invention is preferably Portlandcement, however any of the cements commonly used in oil Well cementingoperations such as gypsum cement, the quick-hardening cements andplastic cements appear to be satisfactory.

While I may employ in my composition any volcanic rock which may beexpanded by heating I prefer to use expanded perlite. Expanded perliteis obtained by expanding the volcanic rock of the same name by theMulheisen or the rotary tube process. In such processes the expansiontakes place upon heating during which time the molecular water is drivenoff leaving a light weight, uniform-textured inert mineral substance.The expanded material appears to be composed of small cells containingair or gas and is generally accepted as having the composition ofamorphous aluminum silicate wherein the radical components vary greatly.The perlites that have proven most satisfactory are those derived fromthe so-called tough ores similar to the John Clare ore of Colorado. Theconditions of expansion may be controlled so as to give expandedperlites of controlled size and weight. Although the limiting factor inthe use of the varying sizes of perlite appears to be the size of thepump orifices and the crushing strength of the individual perliteparticles it has been found that sizes up to and including A are mostsatisfactory for use in well drilling cements. Larger sizes of perlitemay, of course, be used depending upon the condition of the well and thehandling equipment. Preferably the perlite should be of a quality whichwill not compress more than 25% of its bulk volume on applications offluid column pressures of 10,000 pounds per square inch. The expandedperlite having graded sizes from 200 mesh to A with substantially equalamounts of fine and large particles appears to be most satisfactory whenits weight is between about 18 to 20 pounds per cubic foot whereas theperlite having particles predominantly between -30 mesh and 12 mesh aremost satisfactory when the weight is maintained between 12 to 15 poundsper cubic foot.

The method of cementing oil wells according to this invention comprisesgenerally the steps of admixing cement and an expanded volcanic rock ina ratio by volume of about 1:01 to 1:8 wth about 0. to 10% of bentoniteby weight of the cement in an amount of water sufiicient to form apumpable slurry and pumping "the resulting admixture into the well hole.The maximum viscosity for pumpability is about 40 poises which may beusually achieved by adding an amount of water equal to about 40% to 90%by weight of the weight of the cement.

The exceptional results which may be had by using the cement compositionand method of my invention will be more apparent from the followingexamples.

EXAMPLE I Hobbs Pool, New Mexico.Well with 7 inch outside diametercasing set 4,008 feet; total depth of well 4,234 feet. A /2 inch outsidediameter with Simplex shoe was set with top of liner at 3,921 feet. 100sacks (100 ft.

of cement were pumped through tubing attached to liner without achievinga shut off. A Baker retrievable retainer was set at 3,810 feet, and 200sacks (200 ft. of cement were pumped into the well on vacuum but failedto cement the liner. 50 sacks (50 ft. of cement with 24 ft. of expandedperlite (graded sizes 30 mesh to 4 inch) was then pumped into well and4,000 lb. squeeze pressure was obtained after all but 1.5 barrels ofslurry were out of the tubing. The latter composition was permitted toset and drilled out satisfactorily.

EXAMPLE II Reeves County, Texus.Cable tool hole with inch casing set at358 feet. The casing was cement with 50 sacks (50 ft. of cement butfilled up with water when hole was drilled. A second 50 sacks of cementwere added with same result. 100 sacks (100 ft. of cement with 36 ft. ofexpanded perlite in graded sizes (200 mesh to A inch) was added.Pressure to 1,500 lbs. was achieved when 40 sacks pumped out. Plug wasdrilled and hole was satisfactory.

EXAMPLE III EXAMPLE IV Monument Pool, New Mexico.This well has 7 inchoutside diameter casing set at 3,777 feet and the total depth of holewas 3,883 feet. The top of liner was set on B. O. T. hanger with packerat 3,739 feet and bottom of liner at 3,892 feet. The liner was cementedwith 100 sacks (100 ft. of cement but without success. The liner wasperforated between 3,841 and 3,844 feet and K Model retainer set abovetop of liner. 150 sacks of cement, with 36 feet of expanded perlite(graded sizes between mesh and A inch) in last 25 sacks, was added andsqueeze pressure raised'to 2,500 lbs. The plug was drilled and wellplaced on production without further perforation.

The usual cement slurry for well cementing purposes is a 44% slurry madeup by adding 5 gallons of water to one sack of cement which containsapproximately 1 ft. and weighs about 94 lbs. Such a slurry will weighapproximately 15.9 lbs. per gallon. The addition of representativeamounts of perlite and bentonite to such a slurry will change the weightas shown in Table I below:

Table l 44% CEMENT SLURRY WEIGHT Percent by volume of expanded With 0%With 3% With 5% perlite to volume of cement Bentonite BentoniteBentonite The above weights were made by means of a Baroid mud scale,after mixing for 1 hour.

A slurry containing perlite with or without bentonite added to cementand having a weight of 10 lbs. per gallon will have a reduction inpressure head of 37% over a 44% or 15.8 lb. slurry which means that acolumn of cement at 10 lbs/gal. can be raised 49.5% higher with the samepressure than can a 15.8 lb./ gal. slurry. This reduces the pressure onthe formation accordingly and descreases the tendency of the cement tobe lost into porous formations for any given height of cement.

Comparative apparent viscosities of cement slurries with ordinarybulking agents and expanded perlite are set out in Table II. Theseviscosities are in terms of poises after one hour mixing in a 44%slurry:

Percentage by weight Redwood fibre Cane fibre Balsawood fibre CellophaneExpanded perlite 1 10% by weight would be approximately 50% by volume.

These comparative viscosities are significant in view of the fact thatthe limit of pumpability or mobility of cement has been found to be inthe neighborhood of 40 poises. Of equal significance is the fact thatthe pumpability of a slurry containing expanded perlite can be increasedby increasing the water cement ratio whereas with the ordinary bulkingagents this does not apply.

In addition to the advantages of resistance to corrosive environments,insulating value, reduction in weight and viscosity, etc., alreadypointed out, the cement composition of my invention is particularlysuitable for certain specialized cementing operations. For example, thecomposition of this invention produces a material when set which is muchless brittle than cements formed by water and cement alone, and isparticularly suited for gun perforating to complete a well. When thismaterial is perforated as is the usual practice in oil well completionit is less liable to shatter and fracture than ordinary cements. Inso-called squeeze cementing jobs the usual practice requires building uppressures with fluid high enough to break down the formation (fractures,etc.) to give room for the cement to be placed and then pumping thecement into the well, however, in 'many cases build up pressures cannotbeobtained because of loss of cement into opemngs made while'br'eakin'gdown the formation.

The cement composition of this invention appears to bridge theseopenings permitting the build up of pressure on thecement job to get thedesired result.

The surprising effectiveness of the cement composition of this inventionas a remedy for lost circulation of drilling fluids, cement slurries andsuch special cement jobs as the aforementioned squeeze cementing appearsto result from a progressive bridging action in which the particles ofexpanded volcanicrock build up across the openings through whichcirculation is lost and are surrounded and agglomerated by the settingaction of the cement. Bridging appears to occur effectively when gradedsizes of expanded volcanic rock having a particle size range up toone-half of the smallest average dimension of the opening to be closedare used.

This progressive bridging action is illustrated by thefollowingexamples.

, EXAMPLE. V Hockley Field, Harris County, Texan-Well with casing set at1660 feet. Circulation of drilling fluid was lost between 4865 feet and4899 feet. At tempts to cement with 100 sacks of cementwith 3% bentoniteand 1% cellophane flakes failed. The well was then cemented with perlitecement containing 6% bentonite according to this invention by pumping aslurry of 25 sacks of cement with 13 sacks of size'D perlite (80% below.065 inch in diameter) and 6% bentonite through the drill pipe followedby a slurry of 25 sacks of cement with 12 sacks of'size C perlite (89%below .065 inch in diameter)"and 6% bentonite and finally followed by aslurry of 25 sacks of cement with 13 sacks of size B perlite (85% below.023 inch in diameter) with 6% bentonite. After the cement had set for'8 hours, the circulation of drillingmud was restored.

. ...EXAMPLE VI Jacksonville, Texas, FieId.The total depth of the wellwas 8730 feet with casing at 8723 and circulation was lost in Rodesaformation at 8626 feet. The'lost circulation was stopped in two stagesof cementing. The first stage was accomplished by pumping into the wella slurry of20- sacks of'cement and 15 sacksof'perlite 'D, followed by 40sacks of cement and 18 sacks of perlite C, and followed by 40 sacks ofcement and 17 sacks of perlite B. These mixtures in the order named werepumped down the drill pipe with a squeeze tool set near the bottom ofthe casing. The second stage was accomplished by pumping a slurry of 20sacks of cement with 9 sacks of perlite D, followed by 20 sacks ofcement and 8 sacks of perlite C and then followed by 10 sacks of cementand 8 sacks of perlite B. This was pumped with the squeeze tool on thedrill pipe set above the perforated zone at 8608-8618 feet. In each casethe slurry with the largest size of perlite was pumped into the wellfirst and the smallest last. Tests showed that loss of cement anddrilling fluid was stopped and the casing was satisfactory.

While I have attempted to explain the effectiveness of my cementcomposition and method of cementing oil wells on the basis of theorieswhich seem consistent with observed facts, I do not bind myself to suchtheories. Accordingly it will be understood that while I haveillustrated and described a present preferred embodiment of myinvention, it may be otherwise embodied or practiced within the scope ofthe following claims.

I claim:

1. A composition for use in cementing oil and gas wells or the likecomprising about equal volumes of cement and expanded perlite and about5% of bentonite by weight of the weight of the cement.

2. A'slurry for use in cementing oil and gas wells or the likecomprising a mixture of equal volumes of cement and expanded perlite andabout 5% by weight of bentonite on the weight of the cement in amount ofwater equal to about 40-90% by weight of the cement.

3. The method of cementing oil and gas wells or the like comprisingadmixing cement and volcanic rock which has been expanded into cellularform by heating in a ratio by volume of between about 1 part cement tofrom about 0.1 part to 8 parts expanded volcanic rock in watier1 andpumping the resulting admixture into the well 4. The method of cementingoil and gas wells or the lik'e'comprising admixing cementand volcanicrock which has been expanded into cellular form by heating, in a ratioby volume of between about 1 part cement to from about 0.1 part to 8parts expanded-'volcanic-rock and up to about 10% bentonite by weight ofthe weight of the cement in water and pumping the resulting'admixtureinto the well hole.

5. The method of cementing oil and gas-wells 'or the like comprisingadmixing cement and volcanic rockwhich has been expanded into cellularform by heating in a ratio by volume of between about 1 part cement tofrom about 0.1 part to 2 parts expanded volcanic rock and up to about10% bentonite by weight of the weight of the cement. i 1 3 6. The methodof cementing oil and gaswells' orthe like comprising admixing cement andperlite ina ratio by volume of between about 1 part cement-to from about0.5 part to 2 parts expanded perlite in water and pumping the resultingadmixture into the well hole.

7. The method of cementing oil and gas Wells or the like comprisingadmixing cement and perlite in a ratio by volume of between about 1 partcement to from about 0.1 part to 8 parts expanded perlite and up toabout 10% bentonite by weight of the weight of the cement'and pumpingthe resulting admixture into the well hole. v

8. The method of cementing oil and gas wells which comprises admixingcement and volcanic rock which-has been expanded into cellular form byheating in a ratio by volume of about 1 part cement to from about 0.1part to 8 parts expanded volcanic rock with up to about 10% of bentoniteby weight of the cement in suflicient water tov form a slurry having aviscosity of less than 40 poises and pumping the resulting mixture intothe well hole;

9. A method of cementing oil and gas wells which comprises admixingcement and volcanic rock which has been expanded into cellular form byheating'in a ratioby volume of about 1 part cement to from about-0'.1part to 8 parts expanded volcanic rock with up to about 10% of bentoniteby weight of the cement in an amount of water equal to about 40% toby'weight of the weight of the cement and pumping the resultingadmixture into the well hole.

10. A method of cementing oil and gas wells which comprises admixingcement and expanded perlite in a ratioby volume of about 1 part'cementtofromab'out 0.5 part to 2 parts expanded perlite with up to about 10%bentonite by weight of the cement in water and pumping the resultingadmixture into the well hole.

11. A method of cementing oil and gas wells which comprises admixingcement and expanded perlite of graded sizes in a ratio by volume ofabout 1 to 1 with about 5% of bentonite by weight on the weight of thecement in an amount of water equal to about 40% to 90% by weight of theweight of the cement and pumping the resulting admixture into the wellhole.

12. The method of preventing lost circulation of drilling fluid throughan opening in well hole walls which comprises admixing cement andvolcanic rock which has been expanded into cellular form by heating ofgraded sizes having the range of particle size up to about onehalf ofthe average of the smaller dimensions of the opening in a ratio byvolume of about 1 part cement to from about 0.1 part to 8 parts expandedvolcanic rock with up to about 10% of bentonite by weight on the weightof the cement in suificient water to form a pumpable slurry, pumping theresulting admixture into the well hole and into contact with theopenings in the well hole walls and permitting the admixture to solidifyin said openings.

13. The method of cementing oil and gas wells to prevent lostcirculation of a cement slurry which comprises adding to the slurry anamount of volcanic rock which has been expanded into cellular form byheating equal to a ratio of between about 1 part cement to from about0.1 part to 8 parts expanded volcanic rock by volume on the volume ofthe cement and pumping the resulting slurry into the well hole.

14. The method of cementing oil and gas wells or the like to preventlost circulation through openings in well hole walls, comprisingadmixing cement, volcanic rock particles which have been expanded intocellular form by heating and sufiicient water to form a pumpablemixture, said volcanic rock particles being of suflicient size to bridgethe openings through which circulation is lost, the mixture of cementand expanded volcanic rock being in a ratio by volume of between about 1part cement to from about 0.1 part to 8 parts expanded volcanic Lock,and pumping the resulting admixture into the well ole.

15. The method of cementing oil and gas wells or the like to preventlost circulation through openings in Well hole walls, comprisingadmixing cement, bentonite, volcanic rock particles which have beenexpanded by heating and sufficient water to form a pumpable mixture,said expanded volcanic rock particles being of sufficient size to bridgethe openings through which circulation is lost, the cement and expandedvolcanic rock being in a ratio by volume of between about 1 part cementto from about 0.5 part to 2 parts expanded volcanic rock and thebentonite being up to about 10% by weight of the weight of the cement,and pumping the resulting admixture into the well hole.

16. The method of cementing oil and gas wells or the like to preventlost circulation through openings in Well hole walls, comprisingadmixing cement, expanded perlite which have been expanded into cellularform by heating and sufficient water to form a pumpable mixture, saidparticles being of sufiicient size to bridge the openings through whichcirculation is lost, the mixture of cement and expanded perlite being ina ratio by volume of between about 1 part cement to from about 0.1 to 8parts expanded perlite, and pumping the resulting admixture into thewell hole.

17. The method of cementing oil and gas wells or the like to preventlost circulation through openings in well hole walls, comprisingadmixing cement, bentonite, expanded perlite particles which have beenexpanded by heating and sufficient water to form a pumpable mixture,said expanded perlite particles being of suflicient size to bridge theopenings through which circulation is lost, the cement and expandedperlite being in a ratio by volume of between about 1 part cement tofrom about 0.5 part to 2 parts expanded perlite and the bentonite beingup to about 10% by Weight of the weight of the cement, and pumping theresulting admixture into the well hole.

18. The method of cementing oil and gas wells or the like to preventlost circulation of drilling fluid in well holes which comprisesincorporating into a cement-Water mixture in successive steps expandedparticles of volcanic rock of successively smaller particle sizes whichhas been expanded by heating, pumping the mixture resulting from eachsuccessive addition of volcanic rock into the well hole to bridge theopenings through which circulation is lost.

19. The method of cementing oil and gas wells or the like to preventlost circulation of drilling fluid through openings in the walls of awell hole which comprises successively pumping portions of acement-water slurry into the well hole, into each portion of which,expanded particles of volcanic rock which have been expanded by heatinghave been incorporated, the particles of expanded volcanic rock in eachsuccessive portion being successively smaller in size thereby bridgingthe openings with successively smaller particles.

20. The method of cementing oil and gas wells or the like to preventlost circulation of drilling fluid through openings in the walls of awell hole which comprises successively pumping portions of acement-water slurry into thewell hole, into each portion of which,expanded particles of perlite which have been expanded by heating havebeen incorporated, the particles of expanded perlite in each successiveportion being successively smaller in size thereby bridging the openingswith successively smaller particles.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,770,767 Collings et al. July 15, 1930 1,807,082 Boynton May26, 1931 1,885,731 v Kraus Nov. 1, 1932 2,041,086 OBrien May 19, 19362,079,518 McQuiston May 4, 1937 2,206,677 Shepler July 2, 1940 2,288,557Vollmer June 30, 1942 2,326,577 Teague et al Aug. 10, 1943 2,337,295Kennedy Dec. 21, 1943 2,353,372 Stone July 11, 1944 2,561,075 SidwellJuly 7, 1951 OTHER REFERENCES Bureau of Mines Information Circular 7364,Perlite, Sogrge of Synthetic Pumice, August 1946, pages 1-4 an 28gil andGas Journal, July 28, 1949, pages 280, 283,

4. THE METHOD OF CEMENTING OIL AND GAS WELLS OR THE LIKE COMPRISINGADMIXING CEMENT AND VOLCANIC ROCK WHICH HAS BEEN EXPANDED INTO CELLULARFORM BY HEATING, IN A RATIO BY VOLUME OF BETWEEN ABOUT 1 PART CEMENT TOFROM ABOUT 0.1 PART TO 8 PARTS EXPANDED VOLCANIC ROCK AND UP TO ABOUT10% BENTONITE BY WEIGHT OF THE WEIGHT OF THE CEMENT IN WATER AND PUMPINGTHE RESULTING ADMIXTURE INTO THE WELL HOLE.